1. Technical Field
The present invention relates to color balance correction of an image, and more particularly relates to a technology for carrying out desirable color balance correction in response to an attribute of color cast occurring in an image.
2. Description of the Related Art
Where an image is generated through photographing using a digital still camera for example, color cast can occur in which the overall image is affected by a particular color depending on the light source. Generally, color balance correction is performed in order to correct for color cast in an image.
In connection with color balance correction of an image, a technology whereby correction is carried out to ensure that the natural color of human skin is reproduced and that the image as a whole has desirable color balance is described in JP2002-44469A, for example. In this technology, when color balance correction is carried out, correction amounts that ensure that the human skin color expressed in the image will be reproduced with the ideal color for human skin is not used, but rather, correction amounts calculated by multiplying the difference between the skin color expressed in the image and an ideal color by a certain reduction coefficient is used. Using this type of correction, the skin color expressed in the image is corrected such that the skin color will approach the ideal color, and because reduced correction amounts are used, desirable color balance is maintained throughout the entire image.
With regard to color cast occurring in an image, attributes such as an attribute of color regarding which such effect appears and an attribute of degree to which it appears vary depending on the photographing conditions, such as the type of light source. The impressions conveyed to an observer from color cast in an image may vary based on the differences in these attributes. For example, color cast in the green direction that often occurs when photographing is performed under fluorescent light may convey a highly unnatural impression to an observer. On the other hand, the color cast in the orange direction that often occurs when photographing is performed under incandescent light may not convey such a highly unnatural impression. Consequently, the preferred value for the aforementioned reduction coefficient used when performing color balance correction, i.e., the proportion of the correction amount to the difference between the skin color appearing in the image and the ideal color, may vary depending on the attributes of color cast described above.
However, in the above prior art technology, the proportion of the correction amount to the difference between the skin color appearing in the image and the ideal color is fixed, irrespective of the actual color cast attributes. Therefore, it is difficult to perform desirable color balance correction in accordance with the color cast attributes actually observed.
This problem is not limited to images generated using a digital still camera, and is a problem that arises whenever color balance correction of an image is performed.